The invention relates generally to welding techniques, and more particularly to improved processes of detecting and adjusting for poor fit-up between workpieces in such a way that enhances performance, reduces waste, and may reduce rejection of finished parts. The present disclosure is related to previously filed U.S. patent application Ser. No. 13/526,278, entitled “Metal Cored Welding Method and System,” filed on Jun. 18, 2012, which is hereby incorporated into the present disclosure by reference. The present disclosure also incorporates U.S. patent application Ser. No. 13/681,687, entitled “DC Electrode Negative Rotating Arc Welding Method and System,” filed on Nov. 20, 2012.
A range of techniques have been developed for joining workpieces by welding operations. These include diverse processes and materials, with most modern processes involving arcs developed between a consumable or non-consumable electrode and the workpieces. The processes are often grouped in such categories as constant current processes, constant voltage processes, pulsed processes, and so forth. However, further divisions between these are common, particularly in processes that consume an electrode to add filler metal to the weld. In virtually all such cases, the process selected is highly linked to the filler material and its form, with certain processes exclusively utilizing a particular type of electrode. For example, certain types of metal inert gas (MIG) welding processes, which form part of a larger group sometimes referred to as gas metal arc welding (GMAW).
In GMAW welding, an electrode in the form of a wire is consumed by the progressing weld pool, melted by the heat of an arc between the electrode wire and the workpiece. The wire is continuously fed from a spool through welding gun where a charge is imparted to the wire to create the arc. The electrode configurations used in these processes are often referred to as either solid wire, flux cored or metal cored. Each type is considered to have distinct advantages and disadvantages over the others, and careful adjustments to the welding process and weld settings may be required to optimize their performance. For example, solid wire, while less expensive than the other types, is typically used with inert shielding gases, which can be relatively expensive. Flux cored wires may not require separate shielding gas feeds, but are more expensive than solid wires. Metal cored wires do require shielding gas, but these may be adjusted to mixes that are sometimes less expensive than those required for solid wires.
All three of these electrode types may be used with different transfer modes, referring to the mechanical and electromechanical phenomena of moving metal from the electrode tip to the progressing weld bead. A number of such transfer modes exist, such as short circuit transfer, globular transfer, spray transfer, and pulsed spray transfer. In practice, transfer physics may appear as a hybrid of these, and the actual material transfer may transition between them during welding, although the process and electrode are often selected to maintain a certain transfer mode.
As the torch progresses and consumes the wire it leaves behind a deposit of filler material between the two workpieces known as a weld bead. In general the width of the weld bead created during the transfer mode is seen as a function of several operative parameters. Depending on the fit-up between the work pieces, the weld bead width may or may not be adequate to ensure the integrity of the finished welded product. To avoid this, a welding operator must visually detect the fit-up for any workpiece gaps prior to welding and compensate manually to ensure the integrity of the welded piece. However, automated welding systems lack this intelligent consideration and simply complete welds along a predetermined path in spite of fit-up errors and gaps that may be present. This may result in weld defects, manual reworking, and ultimate rejection of finished welded parts.
Manufacturers are constantly looking for new ways to improve automated welding methods, increase the success rate of the welded pieces, and speed up the manufacturing process overall. However, current automated welding techniques coupled with the increased speed of the processes that manufacturers have come to rely on can result in many finished workpieces with poor fit-up.